Dead simple, absolutely clear, quenches a common thirst (sharing a collection of songs with a friend), can’t-mess-up easy (username, email, password then upload MP3s). For a tiny touch of personality you can change the color of the strip at the top of the screen.
I imagine this could get shut down, but I love the exercise in simple execution. There are so many ways this could have been complicated. Muxtape’s elegance demonstrates the power of sticking to the point.